Is anyone familiar with a design problem or an inherent instability in the #5 intake valve geometry? I have been struggling with my 327 road race motor to find a working combination of cam design, spring design and spring rates that will survive for more than a weekend in a small block. i'm getting closer but...I just returned from a race in Portland. I removed all the rockerrs to do a valve train inspection and again the #5 pushrod has chatter cuts in the top of the pushrod. i have replaced heads and bored and sleeved the lifter bores and changed cams to a relatively mild cam. In the past on this location valves have stuck, pushrods have broke and rockers have been beat up. The only common factor here is the basic design geometry, i have changed everything else. Anybody know of a Chevrolet engineering report on this or an idea of problem.
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Re: Vavletrain instability small Block
if have screw in studs i would use the "step up" type push rod guide plates which put the push rod support closer to the rocker arm helping prevent the distortion of the push rod. http://varelamotorsports.com/engine-...de-plates.html this is the type used on BBC -
Re: Vavletrain instability small Block
If there is some genetic design or oiling deficiency that can cause problems with #5 inlet, Clem would probably know and have a "fix".
As far as I know the design geomtry of all 16 valvetrain sets are the same, which leads to a possible conclusion that there is something dimensionally "out" on your #5 inlet train, or it's not getting enough oil. My hunch is that it's an oiling problem.
Until a definitive answer is found, I suggest you swap in a good pushrod/rocker set from the engine and install a new or good used set in the donner position. This might help determine if there is definitely something wrong with the 5I geometry or oiling or if it was just a random failure.
Do you have piddle valve or edge orifice lifters? The piddle valve are probably best to use on a racing engine since they increase overhead oiling. The edge orifice type overhead oiling is a function of lifter bore clearance, and greater clearance yields increased overhead oiling.
DukeComment
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Re: Vavletrain instability small Block
another thing you want to check if the rocker arm is centered on the valve at full valve lift. if you need to to center the rocker arm on the valve you will need to cut the guide in half and after alignment use wire welder to weld the guide plate back together. isky makes a adjustable guide plate but is is not the raised type to put it closer to the rocker..Comment
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Re: Vavletrain instability small Block
I do use screw in studs(7/16). 5/16 .080 wall thickness hign stregnth push rods I have split guide plates . I spent a lot of time making sure the contact area and location were as good as you can get and then welded the plates together. I have lots of oil to the top. All restrictors have been removed. i have cut groves in the lifter sides to increase the amount of oil to the top and I'm using a rev kit to keep spring pressures low. ( 150# & 320#) All the other rockers are at least last a #5 I is a special problem ,I think?Comment
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Re: Vavletrain instability small Block
any time you take apart the valve train always keep the parts paired up,keep the push rod with the rocker because all have different wear patternsLast edited by Clem Z.; July 20, 2011, 11:42 AM.Comment
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Re: Vavletrain instability small Block
Exhaust side problems are more common than inlet - heat. What's the condition of the rocker and ball. Last sentence of your last post need editing for clarity.
DukeComment
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Re: Vavletrain instability small Block
i was trying to clarify that the problem valve is #5 exhaust not intake. I was running roller tip and trunion at Portland so no ball to examine. My worry is that I'm going to Monterey and i will be running stamped rocker and ball. The chatter marks on the pushrod would have closed off the oil tube if it had continued which would have led to failure. i have to believe its a heat problem that is causing this. I opened up the guide clearance and am not running a seal to make sure that wasn't causing problem. i also route coolant into head from water pump to help cool this area.Comment
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Re: Vavletrain instability small Block
If #5 is running a bit lean for some reason, and the valve to guide clearance is on the low side, I suppose it's possible for the exhaust valve to hang in the guide and hit the piston at high RPM/load. That would cause some very interesting problems.Comment
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Re: Vavletrain instability small Block
Yup, because that cyl may be lean, for some reason. All 8 cyl's never seem to run at the same temps/mixtures and that causes issues.
I know that if you remove the intake manifold divider under the carburetor, (open plenum) mixture distribution becomes less consistant cyl to cyl. (that didn't work well on small blocks, though)Comment
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Re: Vavletrain instability small Block
I forgot that this was an FI engine. That may be a completely different story. One nozzle (#5) could be partially plugged causing a lean condition. It doesn't take much to change the total flow numbers.
Changing the length of the nozzle pipe probably wouldn't change the nozzle flow much.
I used to set these units up on the bench and run solvent through it into (borrowed) baby bottles to make sure flow was equal on all eight nozzles.Comment
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